The present invention relates to the monitoring of an automatic transmission, and in particular the monitoring of downshifts when driving uphill, on a vehicle equipped with an automatic transmission having change laws which already impose on it changes to the lower gear, based on preestablished downshift curves.
When a vehicle equipped with an automatic transmission is traveling uphill, the transmission adapts its operation, in order to provide the driver with more reserve torque. Conventionally, the transmission estimates the slope percentage, and applies a gear change law suited to the slope: when driving uphill, the gear changes are thus performed at higher speed.
However, fine tuning change laws suited to the various road profiles is a complex operation.
For this reason, the publication FR 2 842 579 proposes another method for adapting the operation of an automatic transmission when driving uphill. This method is based on the estimation of the acceleration that the vehicle can potentially reach after an upshift. Such an estimation makes it possible to decide on the opportunity as to whether or not to perform this upshift, if it is requested by the change law applied in the transmission.
According to this publication, the acceleration that can be reached after the gear change is calculated according to the current acceleration, the current engine torque, and the torque difference provided before/after the change. The upshift is then authorized only if the acceleration that can potentially be reached after the gear change is greater than a threshold, called comfort threshold.
The two main drawbacks to this method are on the one hand the weaknesses in the estimation of the acceleration that can be reached after an upshift, and on the other hand the fact that only the upshift gear changes are adapted to the slope. In practice, the downshifts are based either on the change law, or on a loss of speed by lifting the foot criterion, which is difficult to apply.